The present invention relates to an image forming device which is capable of producing an image with toner directly onto a recording element (e.g., a transfer belt) by means of an electric signal (information carrier) and further of transferring and fixing the toner image onto a sheet of transfer paper.
One of the conventional methods for converting an electric signal into a visible image on a recording element (e.g., a sheet of transfer paper) is xerography whereby a latent image is produced by a light recording means and developed with developing powder (hereinafter referred to as "toner"). This method consists of steps for converting an electric signal of image information taken from an original source into a light signal by means of a laser or LED head; exposing to said light signal a photo-sensitive image carrier uniformly charged in advance with statistic electricity; producing a latent image on the photo-sensitive surface according to the light's intensity; letting the toner from the toner carrier make contact with or move on to the latent image to develop the image on the photo-sensitive surface; electrically transferring the toner image to the recording element and then fixing the toner image on the recording element by pressing and/or heating.
Besides the above-mentioned xerography, there is the conventional method of using the combination of an ion generator, a control grid and an image-carrying dielectric drum which conducts the steps of adjusting an ion current passing through the control grid by controlling said control grid according to an electric signal, forming an electrically charged image (latent image) on the dielectric drum in accordance with the electric signal, developing the latent image with toner, transferring the toner of the developed image to a recording element (a sheet of transfer paper) and then fixing the image thereon by pressing and/or heating in the same way as the xerography.
Since the above-mentioned method produces a latent image from the electric signal on the image carrier and develops the latent image with toner, it is necessary to use a writing means for forming the latent image on the image carrier and a means for erasing the used latent image from the image carrier so as to be able to use the latter repeatedly. There is left the problem that the image carrier which usually is made of a photo-sensitive material (e.g., selenium) has the characteristics necessary for forming thereon a latent image but is sensitive to heat and mechanical shocks and contains toxic substances.
Japanese laid open patent publication No. 44457-83 discloses an image-forming method which does not require the use of an image carrier and in which a control grid having two electrodes separated from each other by an insulating layer with openings passing through both electrodes and the insulating layer is placed between a toner carrier (developing tank) and a recording element and a backing electrode is placed on the back of the recording element opposite the side facing the control grid. The first electric field is produced between the toner carrier and the side facing the control electrode, the second electric field is produced between the toner carrier side opening of the control grid and the recording element side electrode and the third electric field is produced between the electrode facing the recording element and the recording element itself. When an electric field is formed within the control grid's opening to allow the toner to pass therethrough from the control electrode facing the toner carrier to the control electrode facing the recording element, the toner particles are transferred to the recording element. At least one of the control electrodes must work with voltage applied thereto for producing a toner attracting force and provided with a means for applying AC voltage for preventing the adhesion of toner particles thereto.
In the above-mentioned method, the adhesion of toner particles to the electrode can be prevented but the adhesion to the insulating wall surfaces within the openings cannot completely be avoided, Consequently, clogging of the grid openings with toner particles may occur making it impossible to form an accurate toner image and also causing the lowering of the printing quality. Frequent cleaning of the control electrodes or replacement of the parts is needed to keep the printing quality at the required level. Maintenace work is difficult and is expensive.
In view of the above-mentioned problems, the present applicant has proposed the provision of an image-forming device which does not require an image carrier such as photo-sensitive material and which also has control electrodes free from the adhesion of toner particles.